1. Field of the Invention
This invention resides in the field of equipment used in the cleaning of storage tanks, and particularly equipment that removes solids or solid-containing materials such as sludge and that is controlled from the tank exterior.
2. Description of the Prior Art
Liquid storage and process tanks tend to accumulate sludge that must be removed periodically to maintain tank capacity. Similar problems occur in large liquid storage tanks in general, including municipal waste systems. Conventional methods of removing sludge from tanks have involved teams of workers entering the tank and removing the sludge by manual labor. This is a highly labor-intensive process with significant economic loss due to the considerable time in which the tank is empty during the cleaning process.
A variety of mechanical devices have been developed to reduce both the cost and the hazards of sludge removal. These devices include baffles built into the tank to guide the collection and movement of the sludge, ports built into the tank wall and floor, rotating rakes to consolidate the sludge and direct it to draw-off pipes, sloped bottoms, and sumps. Disclosures of some of these methods appear in the following United States patents, each of which is incorporated herein by reference in its entirety: Shaffer, R. L., et al. (Ecodyne Corporation), U.S. Pat. No. 3,951,819, issued Apr. 20, 1976; Allen, H. W., U.S. Pat. No. 5,335,395, issued Aug. 9, 1994; Harris, R. B., U.S. Pat. No. 5,830,355, issued Nov. 3, 1998; Allen, H. W., et al., U.S. Pat. No. 6,141,810, issued Nov. 7, 2000; and Sarrouh, S. F. (Parkson Corporation), U.S. Pat. No. 6,234,323 B1, issued May 22, 2001.